JPH05315075A - Forming method for electroluminescence light emitting film - Google Patents

Abstract

PURPOSE:To form a uniform light emitting film by using a base material sulfide object element to serve as a target, and depositing the element in the atmosphere of mixing sulfide gas with sputtering gas. CONSTITUTION:An Sr simple substance is used for a target 20, to mix spatter gas Ar by a state of compound in S and Ce. Ar30 is introduced into a vessel 61 from an introducing pipe 61a through a regulating valve 71 and a flow meter 72. HS40 is mixed with Ar and introduced into the vessel 61 from the introducing pipe 61a through a regulating valve 73 and a flow meter 74. Ce (Ce5H5)3 is heated by a heating means 53 in a generator 52, to circulate Ar30 gasified through a regulating valve 75 and a flow meter 76 and introduced into the vessel 61 from an introducing pipe 61b. A computer 80 controls the regulating valves 71, 73, 75 while supervising detection values of the flow meters 72, 74, 76. An upper part electrode 63 is heated to hold a display panel 10 at about 30 deg.C, and Ce added SrS serves as a base material through sputtering by about 15mTorr, to form a film 14 of emitting EL light in bluish green color.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses sulfides such as Sr, Ca and Zn as a base material to be incorporated in an electroluminescence (hereinafter referred to as EL) display panel having a thin film laminated structure as a base material and rare earths such as Ce, Eu and Pr. The present invention relates to a method for forming an EL light emitting film containing an element as an emission center.

[0002]

2. Description of the Related Art As is well known, an EL display device has a characteristic of self-luminous property, and in particular, an EL display panel having a thin film laminated structure can display a variable image on a large screen with a high density and can display a clear and high brightness image. Since it is possible, its use as a display device for office automation equipment and small computers is rapidly expanding. Many of the EL display panels that have been put into practical use use an EL light-emitting film that emits yellowish green light containing zinc sulfide as a base material and a small amount of manganese as an emission center. It is well known that the structure is as follows. Will be briefly described with reference to FIG.

FIG. 6 is an enlarged sectional view of a peripheral portion of an EL display panel 10 having a thin film laminated structure. Substrate made of transparent glass
A surface electrode film 12 of a transparent conductive film is arranged on the surface of 11 in a striped pattern extending in the front-back direction of the figure in a large number of rows in the left-right direction of the figure, and is covered with an insulating film 13 and then the above-mentioned. The EL light-emitting film 14 made of zinc sulfide or the like containing manganese is formed. After covering this with an insulating film 15, a large number of aluminum back surface electrode films are arranged in the front-rear direction in a stripe pattern extending in the left-right direction. The display of the display panel 10 is performed by applying a display voltage which is switched between positive and negative from the display drive circuit 1 between the front surface electrode films 12 and the rear surface electrode films 16 so that both electrode films 12 and 16 are orthogonal to each other. Since the portion of the light emitting film 14 at each of the intersections emits EL as a pixel on the image display, this is taken out as display light DL from the transparent surface electrode film side.

By the way, since the emission color is naturally limited only by the above-mentioned manganese-added zinc sulfide for the light emitting film 14 and color display cannot be performed, sulfides such as strontium Sr and calcium Ca are used as the base material, and the emission center is EL light-emitting films with various emission colors have been tried by adding rare earth elements such as cerium Ce, europium Eu, and praseodymium Pr as elements, and the film forming methods are roughly classified into electron beam evaporation method, CVD method, and sputtering method. The law is known.

As is well known, in the electron beam evaporation method, an evaporation source in which a luminescence center element is added to a base material is locally heated by an electron beam to rapidly evaporate, and in the CVD method, a base material element and a luminescence center element are contained respectively. In the sputtering method, a gaseous compound is decomposed in the atmosphere such as plasma as a raw material gas, and in the sputtering method, the surface of the base material containing the emission center element is hit by the sputtering gas to fly, and vaporized and decomposed products, respectively. And flying objects are deposited as an EL light emitting film.

[0006]

However, when attempting to form EL light emitting films of various emission colors, each of the above methods has its own problems. The electron beam evaporation method has a track record in forming the above-mentioned manganese-doped zinc sulfide light-emitting film, and the chemical composition of the light-emitting film is more accurate and the distribution of the luminescence center element is more uniform than when the evaporation source is electrically heated. However, when applied to the formation of an EL light-emitting film that uses Sr or Ca sulfide added with a rare earth element as a base material, the rapidly heated evaporation source evaporates in the form of lump particles and remains as it is. Particles with a size of several μm are mixed in the light emitting film because it is easy to deposit, and the surface irregularities become severe, and when a display voltage is applied, the electric field is concentrated on the convex portion of the light emitting film, which insulates the insulating film in contact with it. Destruction is likely to occur. Further, in this method, since the evaporation point of the evaporation source is limited to the local area heated by the electron beam, in a large-area display panel with a diagonal of 20 inches or more, the light emitting film is formed with a uniform film thickness within the surface. It becomes very difficult to film.

In the CVD method, there is no problem that large particles are mixed in the light emitting film, but the biggest problem is that the film forming speed is slow and it is not suitable for mass production. In addition, it is actually not easy to form a large-area light emitting film with uniform film quality by this method. On the other hand, in the sputtering method, the material is ejected from the entire surface of the target in the form of fine particles or molecules and deposited on the light emitting film, so that large particles are not mixed into the light emitting film and a uniform film thickness and film quality with a large area are provided. It is suitable for mass production due to its high film forming speed. Therefore, this sputtering method is considered to be the most promising for forming a light emitting film exhibiting various emission colors.

However, since the vapor pressure of sulfur contained in the sulfide of the base material is high, the sulfur on the target surface is deficient, and the base material formed on the light emitting film has a sulfur deficient composition deviated from the stoichiometric ratio. Since the crystallinity is likely to decrease, it is difficult to form a high brightness light emitting film by the conventional sputtering method. Further, since the sputtering rate differs between the base material and the rare earth element and the concentration of the rare earth element in the light emitting film differs from that of the target, it is difficult to control the rare earth element concentration in the light emitting film. An object of the present invention is to form a light-emitting film of high brightness and various emission colors by utilizing the original advantage of the sputtering method.

[0009]

According to the present invention, as described above, when forming an EL light emitting film containing a rare earth element as a luminescent center with a sulfide as a base material by a sputtering method, the first method is a target. In the second method, the rare earth element compound obtained by mixing the gas of the sulfur compound with the sputtering gas and adding the rare earth element to the target is used in the second method. In the third method, a sulfide base material is used as the target and a gasified rare earth element compound is added to the sputtering gas in the state where the sulfur compound gas is mixed with the sputtering gas Then, the above-mentioned object is achieved by forming a light emitting film.

The above-mentioned sulfides for the base material include SrS and Ca.
ZnS is used in addition to S, and Ce and E are used as rare earth elements for the emission center.
u, Pr, etc. can be used. As the sputtering gas, a usual inert gas such as Ar may be used. First and second
The sulfur compound to be mixed with the sputtering gas by
In addition to H ₂ S, CS ₂ , S (CH ₃ ) ₂ , S (C ₂ H ₅ ) _{2 and the} like can be used. The rare earth element compounds added to the sputtering gas by the first and third methods are Ce (C ₅ H ₅ ) ₃ , Ce (C ₁₁ H ₂₀ O ₂ ) ₃ , Ce (OCH ₃ ) ₃ and its chlorides and fluorides, and Eu (C ₁₁ H ₂₀ O ₂ ) ₃ for Eu compounds.
In addition to its chlorides, fluorides and sulfides, Pr (C ₁₁ H ₂₀ O ₂ ) ₃ as well as its chlorides, fluorides and sulfides can be used for Pr compounds. Can be gasified under the supply of a carrier gas such as Ar and placed on it.

Sputtering is usually tens of mTorr
The high-frequency power for ionizing the sputtering gas is preferably at least 1 kW per panel in order to obtain a deposition rate suitable for mass production of a large-area display panel. It is advantageous to set the temperature of the substrate or panel as the film formation target to about 200-350 ° C to improve the quality of the light-emitting film, and in order to further improve the crystallinity, the temperature corresponding to each base material is usually set. It is desirable to heat-treat.

[0012]

[Operation] The problems of the conventional sputtering method using a base material to which a rare earth element is added to the target are that the sulfur on the target surface is deficient due to the high vapor pressure of sulfur, and the sputtering rate of the rare earth element is the base material. In the first method of the present invention, a sulfur compound and a rare earth element compound are targeted, a sulfur compound is targeted in the second method, and a rare earth element compound is targeted in the third method. Separately, the problem is solved by mixing or adding to the sputtering gas in a gas state.

That is, in the first method, the target is an element for the base material which does not contain sulfur or rare earth elements, and the sulfur gas and the rare earth element compound are mixed or added in a predetermined ratio to the sputtering gas. By performing sputtering in the inside, a sulfide as a base material of the light emitting film is formed with an accurate stoichiometric ratio to improve crystallinity and a rare earth element is added at an accurate and uniform concentration. On the other hand, the second method is suitable when there is no great difference in the sputter rates of the sulfide element and the rare earth element, and the target is the element for the base material to which the rare earth element is added but does not contain sulfur, and the sputtering gas is used. By performing sputtering in an atmosphere in which a sulfur compound gas is mixed at a predetermined ratio, the sulfide base material of the light emitting film is formed with an accurate stoichiometric ratio to improve the crystallinity. Furthermore, the third method is suitable when the element for the base material is, for example, Ca and its vapor pressure does not differ much from that of sulfur, and the sulfide base material is used as the target and the rare earth element compound is added to the sputtering gas. The rare earth element is added to the base material of the light emitting film at an accurate and uniform concentration by performing sputtering in the atmosphere.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. 1 and 2 are configuration diagrams showing a sputtering apparatus and its related apparatus for carrying out the first and second methods of the present invention, respectively, and FIG. 3 is a light emission characteristic diagram of a light emitting film formed by both methods. FIG. 4 is a configuration diagram showing a sputtering apparatus and related apparatus when carrying out the third method of the present invention, and FIG. 5 is a light emission characteristic diagram of a light emitting film formed by the third method.

The sputtering apparatus 60 shown in the right half of FIG. 1 can be commonly used in any of the first to third methods of the present invention, and as shown in FIG. It is provided with a lower electrode 62 and an upper electrode 63, and is constructed so that the gas can be introduced from the introduction pipes 61a and 61b after the inside of the exhaust pipe 64 is pulled to a high vacuum V. The lower electrode 62 on which the target 20 is mounted is insulated from the container 61 by the insulation 62a, and high frequency power is supplied from the high frequency power supply 65 to the container 61 through the matching circuit 66. The upper electrode 63 to which the display panel 10 of FIG. 6 is attached is provided with a heating means, and the light emitting film 14 is formed on the lower surface of the upper electrode 63 while keeping the display panel 10 at a predetermined temperature.

Before the light emitting film 14 is formed, the display panel 10 is provided with a transparent conductive film such as ITO as the surface electrode film 12 on the transparent glass substrate 11 as described with reference to FIG. For example, it is provided with a film thickness of 0.2 μm and is covered with an insulating film 13 of silicon nitride or the like with a film thickness of about 0.3 μm. After the light emitting film 14 is formed, the light emitting film 14 is covered with an insulating film 15 having a thickness of 0.3 μm, such as silicon nitride, and heat-treated at a predetermined temperature.
It is assumed that the thin film laminated structure of the display panel 10 is completed as shown in FIG. 6 by disposing the aluminum back electrode film 16 having a film thickness of 0.5 μm, for example, after it is applied to 14.

In the embodiment shown in FIG. 1, a light emitting film 14 for emitting EL in blue-green light having a wavelength of 450 nm is formed by using Ce-added SrS as a base material. In this first method, a base material is used as a target 20. A simple substance of Sr which is an element to be sulfurized is used, and sulfur S and Ce of the rare earth element are mixed or added in the form of compound gas to the sputtering gas which is usually Ar. A gas supply system 70 for this purpose is shown on the left side of the figure. Argon 30 for the sputtering gas SG is introduced from the cylinder 31 through the adjusting valve 71 and the flow meter 72 into the container 61 through the introduction pipe 61a.
Hydrogen sulfide 40 may be used as the sulfur compound, and it is mixed with the sputtering gas SG from the cylinder 41 therefor via the adjusting valve 73 and the flow meter 74 and introduced into the container 61 through the introduction pipe 61a. The sputtering gas SG is not limited to argon, but various inert gases are used, and the sulfur source for the base material is not limited to hydrogen sulfide, CS ₂ , S (CH ₃ ) ₂ , S (C ₂ H ₅ ) _2, etc. The gaseous compound of 1 can be used if necessary.

In this example, triscyclopentadienyl cerium Ce (C ₅ H ₅ ) ₃ was used as the rare earth element compound,
This is heated to 400 ° C. in the gas generator 52 by the heating means 53, and argon 30 as the carrier gas CG is gasified by passing it through the adjusting valve 75 and the flow meter 76 to make it gas from the introducing pipe 61b. Introduce to 61. Further, in this embodiment, a control computer 80, which is a simple microprocessor for controlling the gas supply system 70, is provided to control the regulating valves 71, 73, 75 while monitoring the detection values of the flow meters 72, 74, 76. To do. When supplying the sputtering gas SG at a flow rate of, for example, 40 cc / min., It is preferable to control the flow rate of hydrogen sulfide 40 to about 15 cc / min. The flow rate of the carrier gas CG is controlled according to the concentration of the rare earth element added to the base material of the light emitting film 14, and in this embodiment Ce
The carrier gas CG is supplied at a flow rate of 5 cc / min. To make the concentration of 0.5 wt%.

The light emitting film 14 is formed by sputtering under the conditions that the upper electrode 63 is heated to keep the temperature of the display panel 10 at about 300 ° C. and the atmospheric pressure in the container 61 is kept at about 15 mTorr. High frequency power is displayed on the display panel 10 diagonally 20
In the case of a large area of about inch, it is better to set it to 1kW or more.
FIG. 3 shows the light emission characteristic A1 of the display panel 10 in which the light emitting film 14 is formed to a film thickness of 0.6 μm by the first method, in comparison with the conventional characteristic B1. The Ce concentration in the base material of the light emitting film 14 according to the first method is 0.5 wt%, and the sample according to the conventional method has the same thickness as the light emitting film formed by the sputtering method using SrS to which Ce is added to the same concentration. did. The horizontal axis of FIG. 3 is the display voltage DV, and the vertical axis is the emission luminance I. As shown in the figure, the emission threshold is changed from 190V in the conventional method to 160V in the first method, and it was difficult to achieve an emission luminance of 100 cd / m ^{2 in} the conventional method, but high luminance of 200 cd / m ² or more in the first method. Is obtained.

A display panel 10 having the emission characteristic A1 shown in FIG.
When the light-emitting film 14 was analyzed, it was confirmed that the stoichiometric ratio of Sr to S in SrS of the base material was close to 1, and the result of X-ray diffraction showed that the crystallinity of the base material was much better than before. It was confirmed. In addition, the Ce content in the base metal was almost as expected.
At 0.5 wt%, it is considered that the concentration distribution in the thickness direction of the light emitting film 14 is sufficiently uniform. The film forming rate is sufficiently high because it is a sputtering method, and it is suitable for mass production without problems.

Although Ce (C ₅ H ₅ ) ₃ was used as the rare earth element source in the above-mentioned examples, in addition to this, Ce (C ₁₁ H ₂₀ O ₂ ) ₃
A cerium organic compound such as or Ce (OCH ₃ ) ₃ or a chloride or fluoride of Ce can be used. When Eu or Pr is used as the rare earth element, Eu (C ₁₁ H ₂₀ O ₂ ) ₃ or P as trisdipivaloylmethanate is used as in the case of Ce.
r (C ₁₁ H ₂₀ O ₂ ) ₃ can be used, or their chlorides, fluorides, sulfides, etc. can be used. Of course, the heating temperature for gasifying these is set according to the type of compound.

FIG. 2 shows an embodiment of the second method. Also in this embodiment, the light emitting film 14 having SrS added with Ce as a base material is formed, but in the second method, a rare earth element is used as the target 21.
Sputtering gas in which sulfur for the base material is used in the form of a compound such as H ₂ S by using the one in which Ce is added to the sulfuration target element Sr for the base material.
Mix with SG. The argon gas 30 for the sputtering gas SG and the gas supply system 70 for this hydrogen sulfide 40 shown in FIG. 2 are simply the structure of FIG. Also in this second method, Eu and Pr can be used as the rare earth element in addition to Ce, but in the present embodiment, Sr containing 0.2% Ce is targeted.
21, 25% H ₂ S was mixed with the sputtering gas SG, and the temperature of the panel 10 was 300 ° C. and 15 mTo as in the previous example.
The light-emitting film 14 is formed by sputtering with a high-frequency power of 2 kW under the atmospheric pressure of rr.

FIG. 3 shows a light emission characteristic A2 of the display panel 10 in which the light emitting film 14 is formed to a film thickness of 0.6 μm according to the embodiment. As can be seen from the figure, the light emission threshold value is comparable to that of the first method, but the light emission threshold is smaller than that of the first method because the addition amount of Ce, which is the emission center element, is small. The brightness I is low. However, the emission luminance I is higher than that of the conventional emission characteristic B1 in which the amount of Ce added is large, and it is possible to display at a luminance of 100 cd / m ² . In the second method, it is difficult to increase the amount of the rare earth element added as in the first method, but there is an advantage that the film formation is easy. The target used in the second method can be easily prepared in the form of an alloy of Sr and a rare earth element or a mixed sintered body of Sr and a rare earth element or a compound thereof.

FIG. 4 shows an embodiment of the third method. In the third method, a sulfide base material is used as a target and a rare earth element compound is gasified and added to the sputtering gas. In this embodiment, CaS containing Eu is used as a base material, and EL emission is performed in red at a wavelength of 660 nm. In order to form the light-emitting film 14 to be used, the base material CaS is used as the target 22 and Eu is used as the sputtering gas SG.
Europium chloride is added as a compound. For this reason,
For example, the sputtering gas SG of Ar is supplied from the gas supply system 70 to 30
The carrier gas CG is supplied at a flow rate of about 3 cc / min. to the europium chloride 51 heated to 600 ° C. in the gas generator 52 to be gasified and added to the sputtering gas SG. ..

The light emitting film 14 is formed by heating the display panel 10 to about 250 ° C. and performing sputtering under the conditions of an atmospheric pressure of about 20 mTorr. As a result, a light-emitting film with a Eu concentration of 0.1 wt%
Emission characteristics A of the display panel 10 in which 14 is formed with a film thickness of 0.6 μm
3 is shown in FIG. Characteristic B3 for comparison is C containing the same concentration of Eu
This is a case where the light emitting film is formed to have the same film thickness by the conventional method using aS as a target. According to the third method, as can be seen from the figure, the light emission threshold value becomes 140 V or less from the conventional 155 V, and it is difficult to emit light of 100 cd / m ^{2 in} the conventional method, but it is as high as 200 cd / m ² . Brightness display is possible. Note that the third method is limited in application when the vapor pressure of the element to be sulfurized is not so different from that of sulfur, but has an advantage that film formation is easier than the first method. Of course, in addition to the above-mentioned Eu, Ce, Pr or the like can be used as the rare earth element.

[0026]

As described above, according to the first method of the present invention, the target element is the element to be sulfurized for the base material, the sulfur compound gas is mixed with the sputtering gas, and the gasified rare earth element compound is added. In the method of 1, the target element is a sulfurization target element to which a rare earth element is added, and the sulfur compound gas is mixed with the sputtering gas. In the third method, the target is a sulfide base material and is gasified into the sputtering gas. The following effects can be obtained by adding a rare earth element compound and forming an EL light emitting film by a sputtering method.

(A) In the first method, both the sulfur for the base material and the rare earth element for the emission center element can be supplied together with the film formation rate in the state of compound gas. It is possible to improve the crystallinity by adding the sulfide of the above in a precise stoichiometric ratio and to add the rare earth element in an accurate and uniform concentration. (b) The second method is suitable when there is no large difference in the sputtering rate between the sulfide element and the rare earth element, and the EL emission is achieved by supplying sulfur for the base material in the form of a compound gas together with the film formation rate. The sulfide base material of the film can be formed with an accurate stoichiometric ratio to improve the crystallinity.

(C) The third method is suitable when the vapor pressure of the element for the base material is not much different from that of sulfur, and the rare earth element for the emission center element is supplied in the state of the compound gas together with the film formation rate. By doing so, the rare earth element can be added to the EL light emitting film in an accurate and uniform concentration.

Any of these methods of the present application has the effect of forming an EL light emitting film having a higher emission brightness than conventional ones, a large area light emitting film can be formed with a uniform film thickness and film quality, and the film forming speed is high. Therefore, it is suitable for mass production of EL display panels. The method of the present application is particularly suitable for film formation when various emission colors are given to the EL light-emitting film by selecting the base material and the emission center element. Can contribute to the expansion of.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a sputtering apparatus and related apparatus suitable for carrying out a first film forming method of an EL light emitting film of the present invention.

FIG. 2 is a configuration diagram of a sputtering apparatus and related apparatus suitable for carrying out a second method for forming an EL light emitting film of the present invention.

FIG. 3 is a characteristic diagram showing a light emission characteristic of a display panel on which an EL light emitting film is formed by the first and second film forming methods, in comparison with a light emission characteristic by a conventional method.

FIG. 4 is a configuration diagram of a sputtering apparatus and related apparatus suitable for carrying out the first method for forming an EL light emitting film of the present invention.

FIG. 5 is a characteristic diagram showing light emission characteristics of a display panel on which a light emitting film is formed by a third film forming method, in comparison with light emission characteristics by a conventional method.

FIG. 6 is a cross-sectional view of a display panel to which a method for forming an EL light emitting film is applied.

[Explanation of symbols]

10 EL display panel 14 EL light emitting film 20 Strontium as a target 21 Cerium-containing strontium as a target 22 Calcium sulfide as a target 30 Argon for sputtering gas 40 Hydrogen sulfide as a sulfur compound 50 Ce (C ₅ as a rare earth element compound H ₅ ) ₃ 51 Europium chloride as a rare earth element compound 52 Gas generator for gasification of rare earth element compounds 60 Sputtering device 70 Gas supply system A1 EL emission characteristics by the first film forming method A2 Second film forming method EL emission characteristics due to A3 EL emission characteristics due to the third film formation method CG Carrier gas DV Display voltage I EL emission brightness SG Sputtering gas

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuki Shibata 1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Fuji Electric Co., Ltd.

Claims (3)

[Claims] 1. A method for forming an electroluminescent light-emitting film containing a rare earth element as a luminescent center by using a sulfide as a base material by a sputtering method, wherein a sulfur compound is used as a sputtering gas with a target sulfurating element for the base material. A method for forming an electroluminescent light-emitting film, which comprises depositing the light-emitting film in a sputtering atmosphere to which a gas is mixed and a gasified compound of a rare earth element is added. 2. A method for forming an electroluminescent light-emitting film containing a rare earth element as a luminescent center using a sulfide as a base material by a sputtering method, wherein a sulfuration target element for a base material to which a rare earth element is added is used. A method for forming an electroluminescent light emitting film, comprising depositing the light emitting film as a target in a sputtering atmosphere in which a sulfur compound gas is mixed with a sputtering gas. 3. A method for forming an electroluminescent light-emitting film containing a rare earth element as a luminescent center using sulfide as a base material by a sputtering method, wherein rare earth gasified into a sputtering gas by using the sulfide base material as a target. A method for forming an electroluminescent light emitting film, comprising depositing the light emitting film in a sputtering atmosphere to which a compound of a similar element is added.